Long-Term Autoimmune Risk Following Pediatric Acute Pyelonephritis: A Nationwide Cohort Study

Introduction: Acute pyelonephritis (APN) is a serious bacterial infection requiring hospitalization during childhood. This study investigated whether hospitalization for APN is associated with increased subsequent autoimmune disease risk. Methods: In this nationwide, population-based retrospective cohort study using the Korean National Health Insurance Service database, we included children born between 2002 and 2005. Children hospitalized for APN (identified by inpatient ICD-10 codes) were matched by birth year and sex to controls without APN. Clinical data including microbiological outcomes were unavailable. The primary outcome was incident autoimmune disease after a 1-year lag period. Results: The study included 31,856 children with APN and 318,560 matched controls. Autoimmune disease incidence was 98.35 and 59.91 per 10,000 person-years, respectively. APN was associated with increased risk, with heterogeneity across diseases; the strongest association was for IgA nephropathy (aHR 2.14; 95% CI 1.92–2.29). Risks were elevated for autoimmune thyroiditis, Behçet disease, and acute disseminated encephalomyelitis. Recurrent APN carried higher risk than a single episode. Conclusions: Hospitalization for childhood APN was associated with increased autoimmune disease risk through early adolescence. The stronger association with recurrence suggests a dose–response relationship. However, exposure misclassification, unmeasured urinary tract anomalies, and antibiotic-related microbiome effects limit causal inference.